Execute Direct Access Program: Difference between revisions

Revision as of 00:16, 13 May 2011

Revision as of 02:22, 13 May 2011

Line 12:

XDAP must reference an OPENed DCB and a full direct access record identifier. The DCB may be OPENed for input, for output or for input and output, but all outputs must be update writes of existing records as XDAP does not support format writes. BSAM and BPAM are available for executing format writes (writes which add new records to the dataset).

The IOBSPSVC flag (logically, the '''IOB''''s '''S'''AM and '''P'''AM '''SVC''' flag) is available which causes SAM and PAM appendages to be bypassed. This enhancement, which was implemented with SVS, but was not retrofitted to previous versions of the OS, facilitates processing a dataset OPENed for BSAM or BPAM while using XDAP. Otherwise, SAM and PAM appendages could cause random lowsupervisor storage overlays when presented with a generalized or possibly ill-formed XDAP channel program. An obvious circumvention, for pre-SVS systems, is to use only those XDAP channel programs which do not utilize RPS (rotation position sensing).

[[Category:IBM Mainframe computer operating systems]]